A three dimensional structure can be used as the reinforcing skeleton for a composite load bearing structure. The sizes of structures required by industry are such that fairly large weft insertion devices are needed to insert the weft. However, all the yarns must be very closely packed in the final structure to achieve the high strength required for most applications. In U.S. Pat. No. 5,449,025 to Weinberg a method is described whereby warp threads are opened into a shed using a rotating reed to enable the weft to be inserted at the widest opening of the warp. This weft is trapped by closing the warp by rotating the reed back to its original position and the weft is then beaten up into the structure. There are applications where the ratio of the warp spacing required during weft insertion and in the final structure is particularly large, such as between 5 and 10 to one. It is difficult to obtain such a ratio using a rotating reed.